Chapter 22.4

Nuclear Fission and Nuclear Fusion

Objectives:1.Define nuclear fission, chain reaction, and

nuclear fusion, and distinguish between them.

2.Explain how a fission reaction is used to generate power.

3.Discuss the possible benefits and the current difficulty of controlling fusion reactions.

Nuclear Fission• In nuclear fission, a very heavy nucleus

splits into more-stable nuclei of intermediate mass.

• Enormous amounts of energy are released.

• Nuclear fission can occur spontaneously or when nuclei are bombarded by particles.

• A chain reaction is a reaction in which the material that starts the reaction is also one of the products and can start another reaction.

• The minimum amount of nuclide that provides the number of neutrons needed to sustain a chain reaction is called the critical mass.

• Nuclear reactors use controlled-fission chain reactions to produce energy and radioactive nuclides.

Nuclear Chain Reaction

Nuclear Power Plants• Nuclear power plants use energy as heat from

nuclear reactors to produce electrical energy.

• They have five main components: shielding, fuel, control rods, moderator, and coolant.

1.Shielding is radiation-absorbing material that is used to decrease exposure to radiation, especially gamma rays, from nuclear reactors.

2.Uranium-235 is typically used as the fissile fuel.

3. The coolant absorbs the energy as heat that is produced

4. Control rods are neutron-absorbing rods that help control the reaction by limiting the number of free neutrons

5. A moderator is used to slow down the fast neutrons produced by fission.

Nuclear Power Plant Model

Nuclear Fusion• In nuclear fusion, low-mass nuclei combine

to form a heavier, more stable nucleus.

• Nuclear fusion releases even more energy per gram of fuel than nuclear fission.

• If fusion reactions can be controlled, they could be used for energy generation.